Pass in correct "singleColumn" prop value when auto-columns is not used.

app/javascript/mastodon/is_mobile.js

@@ -1,7 +1,14 @@
 const LAYOUT_BREAKPOINT = 1024;
 
-export function isMobile(width) {
-  return width <= LAYOUT_BREAKPOINT;
+export function isMobile(width, columns) {
+  switch (columns) {
+  case "multiple":
+    return false;
+  case "single":
+    return true;
+  default:
+    return width <= LAYOUT_BREAKPOINT;
+  }
 };
 
 const iOS = /iPad|iPhone|iPod/.test(navigator.userAgent) && !window.MSStream;